The long-term goal is to better understand, explain and predict self-motion perception and misperception for three-dimensional motions, particularly without vision. Spatial disorientation and misperception of self- motion are primary symptoms of vestibular disorders. In some cases, the misperceived motion correlates more with the disorder than do the commonly-studied pathological eye movements. However, our scientific understanding of human self-motion misperception has mainly been concentrated in the past on simple motions. The current project focuses on self-motion perception in healthy subjects during complex motions. The first aim is to identify, and to advance the tools for identifying, components of self-motion misperception that are due to the three-dimensional physics of linear-angular interaction, and those that are due to peculiarities of the physiological system. For complex motions, it is easy to accidentally attribute perceptual phenomena to anomalies of the physiological system when, in fact, the perception can be explained by the acceleration stimulus. Computer modeling will be used, and existing data on roll-tilt perception in a centrifuge will be compared with physics-based models to test the hypothesis that perception of roll tilt change can be explained in a straightforward way by the three-dimensional laws of motion. Three- dimensional animations will also identify motion components not yet tested experimentally. The second aim is to determine whether self-motion perception deviates in a logical way from the standard "linear" theory. Tested will be the hypothesis that self-motion perception tends, instead, toward simple and familiar motions. Experiments with combined tilt and translation of subjects will be performed and compared with computer simulations, to determine whether perception follows that predicted by standard eye-movement models, or whether perception tends more toward simple tilt-translation motions. The results will give a better means of explaining and predicting complex self-motion perception. An additional outcome of this project will be the availability of three-dimensional computer animations to aid in subject reporting, and analysis, of self-motion perception. Measures of misperceived motion or orientation provide a promising arena for diagnostic testing for vestibular disorders. This project will provide tools and analyses for complex self-motion perception. [unreadable] [unreadable] [unreadable]